Yes from me.

As you can see, there's a safe spot for Boss1 and also for last Boss.

So for Gti, i think the specific rules you enter are not exact (sorry i didn't explain well) : "- Only BIG damages get you hit and destroy your shield. (Use of Cheat code is disallowed and can be verified as follow: With default bullet damage the shield stays to max; With big bullets not)."

=> sometimes in the game, when you get hit by a default bullet, the shield and the mecha get hit... that's why it's weird :(
i think you should explain like that :
In general, only BIG damages get you hit and destroy your shield. It depend where your mecha get hit.
(Use of Cheat code is disallowed and can be verified as follow: With default bullet damage the shield could stays to max; With big bullets not)."

Another idea is sometimes, maybe shield need 2 hits for go down ?

For the damage, i think it also (maybe) depend of the hitbox where the Mecha get hit. I made some online search but found nothing. it looks like i'm the first one to show multiple loops on video ?

Some others explanations (i forgot) : When you start a new loop, the game will give you the Laser weapon at the maximal power. that's also normal. When you check the second loop @ 19:45, you can see i take a big damage from the Boss but the shield stay full... So why ? For be clear, i don't know ! But i think the new loops are easier than the first one. Maybe there's some extra Shield or something... But as i show at the 5th loop, i'm not invincible :p
For people who ask : new loop = that's not new harder difficulty, there's not more enemies or something. The game looks like EXACTLY same than the first loop ! (except the laser weapon at start and the "extra shield"), i didn't notice any other changes...

Thanks for the detailed explanation. I've copied it over in the SPECIFIC RULES.

RULES need to be changed !

This game is weird, so it need some explanations !
First when you finish the stage 5, you will see the ending. After that, when "Jaleco" logo appear, you can press "Select" Button. You will be able to restart the game (and then make a new loop).
That's cool right ?

But, there's three importants things to know in this game !
- This game has an auto fire by design. So that's normal !
- The damage shield is 8 for maximal protection (and better bonus score).
When you take a hit, sometimes, it don't go down ! At the beginning, i thought i enable something like cheat code or game is bugged... but no, that's normal !! Only some BIG damages get you hit and destroy shield.
- There's a cheat code you can enable during the title screen and make you invincible. You can see the demonstration i made here :
https://www.youtube.com/watch?v=22pcqXQDRso


So how to do for be sure the player don't use the cheat code.
The solution i found is to take damage at the boss 2 (or before but because the game is easy...).
As you can see, @ 3:47, i take a bullet damage and shield stay to max !
But if i take damage from the big bullets, here you can see the shield goes down. That's mean there's no cheat code used !
Second thing for be sure is at the last loop you wanna do, start a last one without kill enemies and try to die. If the shield also take damage, that's mean the run score is ok (@ 49:37) :p
(that's my idea for prove score run is legit)