will I lose the pre-exercises if I never work on them?

I have a question that bothered me since weeks and so I thought I am just going to ask it here.

Foundation Course is great, I love working out and I make good progress.

Now, here is what I don't really understand or what leaves me a little stumped.

In the Foundation work, the intensity builds up gradually. So bent hollow holds-> straddle hollow holds-> straddle hollow rocks->hollow holds->hollow rocks etc.

So I was wondering once I progressed to the next exercises and working on those - won't I lose the ability to do 60 hollow rocks as I never train them?

I mean, Gymnasts do so many different exercises and different cycles. And even Olympians still do hollow rocks!

Hollow Rocks was just an example for my question.

Before Foundation, I always did push-ups with elbows flared out. I could do 40-50 of those. When I started with the tricep push-ups, they were super hard, I could barely do 2. And My shoulders were soo sore! But after just 1 or 2 months I could do 5x15. 
But when I try the push-ups with elbows flared out now - they seems soooo hard! I bet if I would do it for some days I would be able to do 40 again. But yeah, I hope you get my point and can give me some answers!

Exercises that are difficult for you and/or beneficial, you should keep your in your warm ups.

yes- generally it's going to be hard to maintain every ounce of hard earned strength or endurance with a particular movement unless you continue to specifically train for it. I just heard the motivational webinar with coach Sommer and I believe his comment was " you can't have everything."

if you're worried about losing it, do 1 set at mastery as warmup.  You don't have to do it for every exercises, for example if you've mastered hollow body rocks, then doing the bent/straddle variations would be redundant

which exercises do you do in your warm-ups?

Hollow rocks, arch rocks, ring rows, ring dips, hanging leg lifts or straddle ups, single leg squats, natural leg curls, Planche leans