Tail-feather moult
The number of moulted tail-feathers in the winter-quarters is highly variable and subsequently we find large variation in May and June. Advanced individuals show a complete 2nd generation tail, while others return with a clearly suspended moult-stage. In the winter-quarters, many individuals do not proceed the moult of the rectrices in a descendant sequence, since migrating birds in spring really show every conceivable moult-stage (e.g. R5-6 2nd generation, while R1-4 are still juvenile, etc).
Some birds do not show fully-grown rectrices, but it is at least not usual to find a tail in active moult by May and the first half of June. Apart from the obvious fresh white tips, the pattern of the 2nd generation rectrices is mostly juvenile-like, but the darker parts are pure black and the pattern is more vermiculated. However, birds with for example a partially white R2, a nearly complete black R3 and with a R4 showing much white, are common. A small minority shows only very little black on the 2nd generation tail-feathers.
The renewed upper-tail coverts are completely white or with some sparse barring on a white base.

Wing-covert moult
The wing-covert moult has mainly been suspended prior to migration, with in most cases a generation contrast between the inner and outer coverts. This especially applies to the greater coverts, which often show a mix of juvenile and 2nd generation coverts, together with tertials and median coverts which have been renewed. The moult-stage of lesser coverts is more advanced than in the greater coverts, but especially 'upper' lesser coverts are less advanced than the tertials and median coverts.
Regarding the under-wing coverts and axillaries; it is often very difficult to obtain good views to determine the generation. In advanced individuals, these under-wing coverts are already partially or completely renewed and sometimes nearly all-white. It might turn out that the moult of under-wing coverts and coverts show similarity in moult strategy.

Primary moult
The onset of the primary moult in 2nd and 3rd type 2cy LBBGs in early summer is on average slightly later (1-2 weeks) than in typical 1st types. Additionally, the individual variation is more pronounced, with e.g. in the 3rd week of June, birds with only P1-2 missing and birds which already shed P7. However, in comparison with the first type, differences in timing of primary moult is usually not significant.
An interesting phenomenon we encountered, was the sometimes remarkably good condition of the remaining juvenile primaries. In a few cases we experienced real difficulties in determining the generation of the primaries.

Variation in the second type
In short we will discuss the general variation of the 2nd type and its difference from the 1st and 3rd type.

Compared with the first type we already stated that both second and third type usually return to the breeding grounds (northern feeding grounds) with some renewed wing-coverts, tertials and even regularly rectrices. Besides other differences from the first type already covered under the header 'regarding both types', juvenile tail-feathers in this type show less blackish brown patterning on the base of the tail-feathers, causing a less broad but more contrasting tail-band.
Even the under-parts are paler in the second type, with contrasting spots mainly restricted to the flanks and lower hind-neck. The palest parts are the breast and head.  

In comparison with the 3rd type the under-parts are slightly more patterned, especially on the flanks and hind-neck. The 2nd generation upper-parts and wing-coverts show obvious barring and anchor-patterns on a pale or cold brownish grey centre, surrounded by a pale fringe in the second type. The tertials show contrastingly bold brown or blackish barring on a white base (see photo 10 and 11) or only a blackish brown base with a sub-terminal bar sharply demarcated from the pale tip (like third type birds).
Moult-stage and even pattern of renewed feather tracts are on average less advanced than in the third type. The upper-parts seem to be moulted in an earlier stage than the wing-coverts, resulting in a 'wear contrast' between fresher coverts/ tertials against heavier worn scapulars and mantle feathers.

General information regarding the third type and its difference from typical fuscus:
Our knowledge of fuscus is confined to published photographs and limited field observations, but there is little doubt that 3rd types may resemble fuscus superficially. However, we have good reasons to believe this type belongs to intermedius rather than fuscus. To name a few:

1. We have seen every conceivable moult stage (0-100%) in coverts, tertials and tail feathers.
2. Although less often, comparable advanced moult stages occur in the 2nd type.
3. Returning birds with completely or partially moulted primaries (suspended) are very rare.
4. Migration started from the beginning of May onwards, which is too early for fuscus (arriving by July). The latter taxon only rarely reaches northern latitudes in May.

Even if there appear to be intermediate characters, it remains unlikely that birds of this type are a result of hybridisation between both taxa. One would at least expect less high numbers on migration.

As stated earlier, we only have limited experience with fuscus. Based on photographs in various magazines, we think that on colour and pattern of plumage alone, some individuals are hard to separate from typical fuscus. We feel that mahogany brown colours in coverts and tertials are rare in typical 3rd types. In individuals with freshly moulted coverts, the pattern we most often see is a blackish central wedge on a grey brown base, broadening towards the tip, with near the tip some white. Another common pattern is just a diffuse dark shaft on a grey-brown base, and normally with some white near the tip. But remember that patterns may become indistinct or even undetectable when feathers become heavily worn and abraded.

In many birds, the mantle and wing-coverts have been replaced in one wave and in such a case lack any 'wear contrast'. This sometimes results in an already worn and bleached 2nd generation bird.
As shown in the images, typical 3rd types are quite easy to separate from typical 2nd types on plumage colouration and pattern alone. The under-parts are clean white, with only  contrasting spots on hind-neck and flanks. Like the second type, this type shows a paler bill-base. A few birds already have a pale-yellow bill-base. Pale yellow legs have also been noticed in this type, but surely not often.

Other types

Except for these three recognizable types, individuals with serious characteristics of fuscus or with serious characteristics of heuglini turn up in the Netherlands during spring and early summer. Although we call these types simply fuscus-types respectively heuglini-types, this is without the intention of treating these birds as true representatives of both taxa.
It is possible that both types are aberrant individuals from the third or (less probable) second type as discussed above. Lars Jonsson, in his article about identification of fuscus LBBGs (Birding World, 1998) states: "probably the most obvious option is to look for first-summer birds with a new set of flight feathers in July-August." Some of these birds match this feature, as can be seen in image 18.