They make a book that would be great for reading it's called the fundamentals of instruction that describe things never to do to a student (it might be worth reading for some).
Touché
It also gives advice on being clear and unambiguous.
I've apologized for my original "attitude" (complete jerkiness?)
We are trying to help.
You seem to have gone from 50kts to 0 IAS.
"Rotor decay" implies a decreasing (changing) RPM
I think most will agree, in a constant IAS autorotation (autorotation wasn't mentioned in the original question BTW) the RRPM will remain constant.
When changing speeds the RRPM will vary first, and possibly dramatically depending on the rate of IAS change due to the loading/unloading of the disc which causes "flare effect" due to the law of conservation of angular momentum.
Secondarily, once a steady (different) IAS has been achieved and stabilized, the RRPM will stabilize. Potentially at a slightly different RRPM.
Thirdly gross weight and air density will affect what stabilized RRPM will result from a certain collective pitch condition/IAS combination.
My (distant past) experience of R22 autorotations. Suggests the flare effect to be dramatic, and therefore problematic if not taken into account, or beneficial if anticipated and used correctly.
While the difference in RRPMin steady state autorotation at normal speed range. (0-80kts) is undetectable. And masked by the small amount of collective required to maintain the RRPM in the safe range.
In case you haven't been exposed to it yet. The "auto revs" are setup during mtce by varying the "flat pitch" (collective fully down) pitch angle by adjusting the pitch link lengths.
This flat pitch RRPM is designed to be safe at the configuration that produces the lowest steady state RRPM - in this case a very light all up weight. This would result in a RRPM overspeed if a flat pitch autorotation was maintained in an AC at maximum gross weight. Hence the need to have some collective applied to reduce the RRPM to an acceptable level.
Have a great day.