Wise move. I have done the same, only to find out in one case that the older motor file was the more accurate one. Grrrr...
IMO, the motor file proliferation and errors are the biggest threat to the simulation part of this hobby, because they affect each and every flight. We can all give feedback for corrections to kruland and thrustcurve, but it seems to be a bigger challenge than that.
Well, I can speak to this as the Editor of Thrustcurve. To create the files is a very manual process, and yes, occasionally errors are made. We try to fix them asap, but the reality is that this is my hobby too- not a job.
Now, where do errors come from other than a typo type of thing. Well, let me list a few for you. I get my info directly from testing orgs. Let's consider the slight differences in the way they report/measure things. TMT reports propellant weight the difference between ore burn and post burn. From a simulation standpoint this makes total sense. In reality, this may over list the propellant if you were to look at the manufacturers info as you might burn some casting tubes etc.
Then, you can throw I the normal and allowed variation in motors performance. Look it up, but having a ten percent difference motor to motor is possible.
In a motor file, how do you list a motor length? It it the casing length, is it the length of the motor with front and rear closures? Is it the total length including nozzle and forward closures?
Another issue that I think is prevalent is inaccurate simulations. Is your file really accurate? Masses, dimensions, and finish. Have you adjusted your sim for temperature, humidity, wind, and launch angle?
Also, at least for Rocksim and Open Rocket, they are based on Barrowman. If you have not read it there are some qualifications on its use. One commonly exceeded is that Barrowman was intended for subsonic. Anything beyond that is use at your own risk, so to speak. I have, as have others, found that both will work fine up to about Mach 1.5 or so. Again though, the farther you get from Mach 1 the more error you are likely to experience.
So, all that said I think that if you have accurate sim files corrected for actual launch conditions you should be happy if you are within 5-10%.
Do not get me started on dealing with turbulence and base drag in short fat rockets.