How Common Are Silver Half Dollars In "Ordinary" Boxes Of Bank-Rolled Coins?

Last month I described finding 50 silver half dollars in three Loomis boxes that I acquired during a two-week period at two local banks. I think they contained coins from the same collection "dump" because I found more Franklin half dollars (10) plus 90% silver Kennedy half dollars (18) than coins that contain 40% silver in each box. Since then I purchased six more Loomis boxes from the same banks (hoping to find more coins from that "dump") -- but I found only one 40% silver half dollar in them: i.e., one silver coin out of 6,000.

I have been fortunate enough to acquire a box of bank-rolled half dollars that contains 10 more more silver coins from a collection dump every three months or so. I haven't monitored how many silver half dollars I've found in lean ("ordinary") Loomis boxes between those lucky breaks - but I estimate that I find one silver half dollar (a coin that typically contains 40% silver) after searching through 5-10 boxes: i.e., only one silver coin in 5,000-10,000.

Does that ratio sound about right to other experienced CRHs? This kind of information hopefully will encourage new CRHs to be patient as they search for "treasure".