Yeah Sevens, that 469 stamping is puzzling. BUT - back in the mid late 80s and into the early to mid 90s, S&W was trying to sell as many 3rd gen pistols to LE as they could. AND - back then you could get actual gunsmiths to do modifications to your pistol.
You could even order up something special from the Performance Center if you had the money. They did a bunch of customization work to individuals guns back in the early 90s when they first opened the doors. And they also made small bunches of modified standard production guns. I know of two batches of 4566s they did that numbered less than 21 units in the batch.
And then there were all the "one of one" guns that were done by the PC that made there way out the door and into the safes of gunwriters and a few collectors.
So, did an "important customer" or someone in LE who knew someone send in a damaged 469 - and needed the new frame to say 469 for agency recording purposes request that it be done? I can see a few scenarios where it might be needed. And depending on when, there were certainly folks at S&W willing and able to do it.
But could any of this speculation be confirmed, much less documented? Not likely.
But the upside is the OP has a very nice AND unusual 469.
What did Grandma always say about buy the gun, not the story?
I'd buy that nice gun. Regards 18DAI