My take is that there is a difference between institutional records, vs random ad hoc abbreviations that individuals create and use. Those abbreviations may make sense to the person making the notation at the time but, to others might or might not. Meaning, not every written piece of information is relevant. Automatically attaching significance to every instance only creates churn when trying to come to a conclusion. I usually ignore those types of outliers in analysis until I see reoccurrence or pattern.
For instance, an antidote of a hand written “STR” on the inside of a fender could just as easily be the owners initials to identify a part meant for a particular car rather than an official reference to some production group.