It can't have escaped notice that some slipping in attention to details of entry, has occured in recent times.
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For instance, the “check star” isn’t always being included, - I assume we do all bracket an estimate, with a fainter star than the one we're checking?
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Rather suspect, is the procedure of nominating a threshold “comp star” to guesstimate that your star is so many tenths or a magnitude brighter or fainter. Better, just to give a “fainter than” in the case of a threshold sighting?
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Some estimates must be referring to a non AAVSO chart, without giving the source.
Beyond these points, rests the idea that estimates provide interest and guidance for other observers. The loss of “Quick Look” is still to be regretted in this context. “Notes” are no longer up front...in the rare cases where these are even given. The prefixes “Y”; “V” etc, have largely fallen into disuse, too. All militating against communication..... “Aperture and Power”? Yes! Certainly a lost cause, that one.
Certainly questioning the use of just a single comp star for a positive estimate, or failing to cite any comp stars at all (likewise pointless is to list something like "comparison star #8" from a non-AAVSO chart) are valid points and such situations should be avoided in reporting one's observations.
However, concerning item #2 a certain degree of extrapolation beyond the faintest comp star noted in a given sequence may have value if done by an experienced observer. In many instances one can encounter situation where the next fainter comp star in a sequence from the one the observer can detect is a magnitude. or more, deeper and hopelessly beyond the given scope's ability to show it. In such a situation as when the faintest visible comp star is obviously seen and is decidedly above the instrument's threshold, an estimated "fainter than" beyond the faintest visible comp star can be justified. Likewise, there are instances where a sequence gives out at a level brighter than the variable happens to get, yet the variable is visible. There the observer may be left with no other choice than making his estimate by extrapolation.
In my opinion, since particularly in instances of monitoring cataclysmic variables it is of value to report the very faintest possible magnitude that the observer can be sure of, a modest extrapolation is fully justified.
J.Bortle (BRJ)