I'm not sure if this has been a topic for discussion yet, but just think about how nerve racking RE0 would have been if there was the Crimson Head setup just like in Remake? Sends a chill down my spine just to think about them in those tiny train cars..

Crimson Heads would just be too perfect for the sort of gameplay Resident Evil has offered in RE4 and RE5.

True i mean they coulda gotten away with it in say Leech Hunter since its more or less already just a blast fest. Wouldnt have made sense though and would be a major tease.

I would have loved the opportunity to have faced crimson heads in RE0 ~ not sure if there is a more detailed post elsewhere as to why the V-Jolt process is completely omitted from Zero? The mansion zombies may be T-virus infused, whereas the train & facilily zombies were infected from leeches ?

The official reason they were not implemented in Zero is due the fact that there is little to no backtracking in the game, so they decided not to bother with them. I don't necessarily agree with this as you do spend plenty of time in the training facility yet i suppose compared to Remake where practically all the game is backtracking across the mansion, it is a reasonable statement.

Plot wise i guess you could say the zombies in the training facility and factory were only hours old. The zombies in the mansion have been infected since May so the V-act process has had plenty of time to kick in.

Christ man haha its like your capcom itself! Makes perfect sense great observations. And now that I think of it Zero was probably the least zombie heavy in the series (minus the train segment) IMO and yeah even though I never really liked the fact that lickers are apparently zombies double dosed with the T-virus (seems way to simple to be true) that would relate in the way to crimson heads possibly being the post stages of licker transformation I mean the claws, increased mobility, etc.

As always the humble, yet all-knowing Batman sheds light on this, and it's since been pointed out by another expert on PU, Newsbot, that Wesker will enjoy the opportunity to meet the RE0 zombies at the point that the V-ACT process kicks in, during UC ~ The fact that we dont get to incapacitate the RE0 zombies is, in my opinion debatable, because the gameplay allows for them to be downed & burnt with molotovs, and The Batman correctly points out that there is sufficient backtracking for time to elapse for V-ACT ~ I dont think ALL the manision zombies were infected as far back as May (?) We also see Crimson Heads however in the other chapters of UC where their prior zombie incarnation were not as historic as those in the mansion. I believe that initialy this was a continuity error on the part of Capcom, not for the first, or last time.

Of course you incapacitate the zombies in RE0. I'm not sure what he is meaning by this. You shoot them, they go down, they are incapacitated, simple as. What else would you describe them as? The simple answer is that Capcom decided not to implement them in Zero because you don't backtrack as much. That is the only reason. Yes for plot's sake its an obviously natural assumption to suggest that Billy and Rebecca left the facility before V-Act kicked in and it would tie in nicely with Wesker arriving there a few hours later in Beginnings. That makes perfect sense. But saying they simply are not crimson heads because you don't incapacitate them? Makes no sense at all.
The whole process of V-Act kicks in when the host organism loses consciousness ie; when you shoot them and they drop to the floor and the big pool of blood comes out. That, if not killing them, is definitely incapacitating them at least. That's when the virus becomes active again and the transformation begins. So essentially there should have been crimson heads in zero, 2, 3 and CVX but there were not because obviously the idea of crimson heads were not born back then.

The only counterargument to this is simply the length of time they have been infected. The zombies in the mansion {a majority of them at least} had been infected for over two months. This may have something to do with V-Act occuring so quickly. The training facility zombies were only a day or so old at the most, so perhaps they were not infected long enough for the V-Act to occur. This would also explain why they were never found in Raccoon City or Rockfort Island as all the infected in those incidents were only hours or days old, rather than months.

But should they have been in Umbrella's End? Questionable at least. 90% of the research staff had been wiped out, doesn't really leave many survivors to 'incapacitate' them considering there are shit loads of them running about when Chris' team arrives, and the biohazard was less than 3 hours old so it doesn't really leave a lot of time for them to go into a 'dormant state' for the process to occur in the first place.

If i'm rambling, i apologise, it's nearly 3am!

As Batman explained, the reason is in reality, not the RE storyline. Crimson Heads were not in RE0 because of game development reasons, it has nothing to do with the storyline. You can create whatever story to make it fit for you but in the end it is just a design choice.

The Leech zombie replaced it. I must agree, the Crimson Head was better. In my opinion, it was scarier than any boss.