I don't get the way some feel like drugs are the only way to keep muscle. I've never used HGH.
KISS:
If, for example, I added 10lbs of mass on every cycle, I kept about 60% (I'm spit balling here it might have been like that on the first couple later on not so much).
Stop thinking short term. I've said before a bunch of times I've lifted for 40 years this summer. My 1st cycle was around age 37. I averaged 3lbs or so a year with zero gear and 6 pounds with. Aged 18 (started 15) I weighed 175 at the same height I am now. This morning I was 297 (top weight on was 300). I've not used since May/June last year. Still no HGH.
I do what I've always done. I worked to gain (strength for me - muscle for most of you). I'd gain a good amount on and reset my levels up adjusting the before the cycle to what I'd do during and again for what I ought to be now doing after. Same with macros and calories for the before, during and after.
Keep doing that year after year and you end up bigger, stronger and more muscular. Age helps (and is a pain sometimes too). Different jobs, better at stress etc etc.
I'm stronger, bigger and have more muscle than when I was 15 or 18. At a guess I eat more.
Now does HGH help? Sure. But do the other stuff first. If you weighed 200 pre. 210 during and 205 after - that's great. Adjust calories a little, up the weights you use a few pounds from before. Get comfy being 205. Time off between cycles. Then do it all again.