This thread is a great idea, here's my help/feedback:
I opened an issue on Github a few days ago, not realising that Steemd isn't included in the Steem repository: https://github.com/steemit/steem/issues/3082
Expected behavior
When looking up author rewards on Steemd, one would expect that Steemd uses the historic rate of the point in time that the reward was paid out to convert VESTS to SP. For a historic transaction, also historic values should be displayed.
Actual behavior
Instead, Steemd uses the current rate to convert the VESTS to SP and therefore includes the "interest" paid on vested Steem which is not part of the historic reward in my opinion.
One would expect that historic payouts don't change, but the amount of SP displayed increases over time with the current implementation. Also, if the VESTS have been powered down, one has never received the "interest".
How to reproduce:
Look up an author reward on Steemd, write down the SP value and look it up again in a few weeks. Or use beem as demonstrated below.
Recording Of The Bug

Historic value at payout (using beem):
stm = Steem()
start = datetime.strptime('2017-11-27T00:00:00', '%Y-%m-%dT%H:%M:%S')
stop = start-timedelta(days=1)
authoracc = Account("jpphotography")
authorrewardlist = authoracc.history_reverse(start=start, stop=stop, only_ops=['author_reward'])
for reward in authorrewardlist:
timestamp = datetime.strptime(reward['timestamp'], '%Y-%m-%dT%H:%M:%S')
vests = reward['vesting_payout']
sp_payout = round(stm.vests_to_sp(Amount(vests).amount, timestamp=timestamp),3)
print(sp_payout)
returns 0.72