It looks like in some instances you are able to pickup 1 egg and have it count twice.

Here is a clip,

I've been able to reproduce on this egg a few times, but haven't been able to on any others. But i've only tried in a few places.

This also happens on the NES version for the egg at the top of the bridge (2nd egg you get to) at the start of stage 5 with the islands to the point you can shoot it 10 times and still collect it (which results in the collection producing the keycard). I will be looking into replicating this wherever I can for GB as well. I did not have much success with other eggs on NES. Stage 6 overworld would be ideal to really kill some time. Imagine not having to do the last 1-2 rooftops? For the NES, and it seems this egg, it has to do with the position of the egg at the top of the screen.