I was just reading the code last night (for the first time) and independently came to a very very similar conclusion as yours. I believe the easter egg just has an alternate ending... I'm not sold on there being any MORE steps, just a different ending.
Here are a couple things that I've noticed:
"Thundergun_hit" is activated by standing in a certain way near the Gersch. What's especially interesting is that you're not supposed to fire it! How did I figure this? Well, if you look at all the other guns you have to fire (ray gun and crossbow), in that coding, it says
But to activate the "thundergun_hit" flag, it doesn't say "attacker", it says this:
Interesting, huh? So, what I'm saying is that I've come up with the same theory as you in regard to the thundergun standing point blank to the gersch.
Next up, we see that different combinations of these flags produce different results. The flags are "thundergun_hit" (discussed above) and "weapons_combined" (which is ray gun + dolls OR crossbow). Here are the possibilities:
Translation: "thundergun_hit" (standing point blank with PaP thundergun) + "weapons_combined" = ann_egg6 (part 1) complete, but gersch_egg6 will fail. That's okay though, as we'll see what's next.
"Else if" is just an alternate way of going about things. So, this means we can instead just do "weapons_combined" (that means don't do anything in regards to standing point blank with the thundergun). If we just do that, however, notice that last line: "flag_clear (thundergun_hit)". This means that the "thundergun_hit" will be cancelled... The result is that we get "undefined" and "gersch_egg fail"... the undefined probably means that this has no affect on the ann_egg6 (meaning it doesn't cancel the first step we just did )
***[one step here that has to do with the revive part, but I'm gonna leave that omitted for several reasons]***
The final thing we see is this code:
This section dictates the ending of the easter egg. There are three things that can be triggered (all three at once is possible). The first is the Ann easter egg. If all its pieces have been triggered (including that last thing I just discussed), then you get an announcer. Big whoop. Next is the obvious one: Gersch. He babbles a nice thank you, yadda yadda. Third one is plr_num, which I believe checks whether both Ann AND Gersch are activated. You can see that the result of this trigger is some new audio. I suspect it triggers a different dialogue with the characters.
Let me know what you think. I'm down to try this with someone who can capture video. If you don't agree, please don't post unless you have direct criticism on what I've said. Thanks!