Sorry ... the trimsheet design is critical ... the LMC situation depends on what has gone into the error analysis and how much the limits are constrained in association.
A computer calculation has the advantage of being able to do the exercise more accurately etc., but, if the trimsheet is designed by a moderately competent weight control person (nothing difficult in the design .. it just takes a bit of care and good housekeeping), and executed with a modicum of diligence (by the user), the trimsheet CG will be as good functionally as the computer's answer.
Point is, if you dumb down the trimsheet too much, there is no point in having one in the first place .. the only use for a trimsheet is to be able to arrive at an accurate answer a lot quicker than some other way .. otherwise you would use the other way according to your preferences.
Perhaps I should have said something along the lines of "it is pointless comparing LMC figures for different trimsheets or for different Types ?"
It depends on what the allowable LMC limit is before a new W&B is required ..
... means error analysis and limit constraints which went into the design of the sheet ... YOUR 500 kg just happens to be the number for YOUR trimsheet .. now, if one did the job differently (for the same Type) .. the number might easily be 200 kg, or 329 kg .. or whatever.
The only caveat is that an operator could easily adopt a "standard" LMC delta for LMCs across all Types in the operation for standardisation .. but that is not really relevant to your question.
There is just no "one size fits all".
A lot depends on the needs of the operator and load control organisation and, in many instances, the preferences of the sheet designer.
FWIW I've designed somewhere around two hundred trimsheets over the past 35 years or so ... (guess that just means I've just made a lot more mistakes than have most other trimsheet designers ...)