Very unlikely, but these things do (did) happen! Certainly some of my printing errors remain as inexplicable to later viewers - I hope...

It's building castles on sand to try and offer certainties on generalised designs in art, but I think Mike's scenario is perfectly credible. I ran it past Mrs JDK, the art historian, and she thought it interesting and that Mike's suggestion was good. She also added that the artist may have chosen a design to relate to the woman's arms or position, and then done simpler aircraft as it wasn't that strong a part of the composition.

She also says it could be there was a screw-up on the plate and a modified bomber was sketched in to cover it. (She says that's very unlikely, but we all know these things do happen!)

The aircraft formation echoes the similar layout of the '28 new Empire flying boats' poster with more representational Shorts C Class: http://collections.nasm.si.edu/media/full/A19900983000cp02.jpg

In that the tanks just visible seem to be genericised cruiser types, owing something to the Valentine tank, it's not any 'real' tank and not even very like any. Likewise, the rough shape of the majority types echoes the pointed wings and layout of the VA Wellington, but isn't, there's more that's different to the Whitley as there is alike, I'd say.

Also anyone who saw any Whitleys fly, or action photos, would be aware of the very nose down stance of the type, due to the wing having a bizarre angle of attack. Incorporate that in a poster? Probably not, but it's another facet of the real thing not illustrated.

Following Ross' comment, we can observe that pre-war most 'heavy' bombers recognisable to the British artists were twin engine types (the third Briton being the Handley Page Hampden). In fact the wings of the 'other' bombers are more like the Hampden's than the Wellington's, with the straight across leading edge.

Then we've noted that the tail of the solo bomber is 'Hampden like'.

In some '30s stamp design, generic rather than specific was critical, so an artist would incorporate aspects of different aircraft to ensure the aeroplane depicted was credible, but not a real one. We may have something like that going on here. After all, Factory owner A would've cut up rough if the aircraft in the recruitment poster featured aircraft from factory B.

I think my castle is suffering from sand erosion...

Surely the lower right of the leading four planes has a different profile to the others . . . possibly a jet with a radome nose?

Prescient? Or sinister? Or prescient and sinister?

It would make sense if the sequence of the artwork was female figure first, then Zec decided he needed to fit a bomber into that space between her arm and head, as the most difficult spot to fit one in, and planned to scale the others based on that one. After doing that one, he may well have decided it was too much work, and did more stylised planes for the rest.

Of course, forensic graphic art is not my field, so this may be total horseradish - but I do have a Phd so it is plausible total horseradish!