No... there really isn't any point in guessing about its recent history.
You say "having an accurate picture of its history" can help....
The problem is you do not have an "accurate history".
You didn't do the work... are not sure what they did... you suspect they aren't telling the truth... and you think this or that might have happened.
(don't be offended!)
Which means nobody hearing all that can make a diagnosis based on those statements.
They will have to mostly go on the symptoms.
Some of the info is good... some is not very helpful (and can even be misleading).
A good mechanic pretty much listens to what the machine tells him.
............ On to the machine...........
Why is pulling the head such an involved process?
Is it watercooled (does it have radiators) ?
If it is not... and the cylinder head is exposed.. then you can pull the head off and look into the cylinder and put the head back on in 5 or 10 minutes.
And very few of us use torque wrenches for ped heads.. I don't.. (but those of us that have done it a hundred times have a pretty good feel for the correct torque.. if you are the type who breaks things all the time ... then DO use a torque wrench...since this bike is your transportation).
Keep in mind one other thing... as the weather cools off here now in the Northern hemisphere... if the ped is actually too rich... it will start running better and better.
Because the colder the temp... the leaner it gets.
For racing bikes... people generally use one size main for 'normal' temps (say a 100)... and then one size leaner for the hottest days (like a 95)... and one size larger for the coldest (like a 105).
That is a generalization to illustrate a point.
Trying to help. : )