As I said, during the 1980's especially, quality of the grips started to slide, with the major problem being fit.
However, there were occasional problems with even earlier Target grips.
I have a set of VERY early Second Type Target grips as used on the Trooper that are made of a hardwood with a walnut stain finish.
There is the same gap at the bottom rear as shown in the above pictures.
This is not something that happened over night, and there wasn't a year or serial number where grips before that were fine and ones after were bad.
It was a very gradual thing over many years, and NOT a steady progression.
In other words, you'd see individual guns with good grips, guns made during the same time frame with badly fitting grips, and guns made the next year good.
The reason the earlier grips fitted better and more consistently was because Colt took the time to insure the grips fit well.
In later days, grips were simply installed and shipped with little or no effort made to insure a good fit.
Your chances of buying another set of grips and getting a better fit are an absolute crap-shoot.
A better option is to simply re-fit the grips yourself, by opening up the frame pin hole in the lower grip, shifting the grips around until they fit better, then using some 5 minute epoxy in the holes to hold that fit.
(Use some wax on the frame and pin to prevent gluing the grips on.
For an even better fit, you can sand the edges to a tighter fit on the frame, then refinish.
By no means was this a Colt-ONLY thing. S&W's grips also dropped in quality of fit and quality of wood.