If the Pirelli thing comes in, and teams opt for the 3 stopper - which they will....you can rule out any tyre thats done 7 laps or more in used condition.
I believe a used tyre will only be good for 19racing laps. Given the extra 2 laps for in/out lap, and your 1 hot lap, which is 3 laps.
14.75lap equal stints, since you cant do .75 of a lap without crossing your allowance, the stint window is 14laps in equal proportions.
so 19 laps can be your theoretical max stint on a used tyre. 20laps on a new tyre.
To do a 3 stopper, you need a used tyre to be of 5 laps? of max age before you drop into a 4 stop strategy. That writes off a LOT of used tyres for a lot of drivers.
19 allowed laps on a used tyre (unless you have a tyre with 2 laps on it - which some drivers do)
14 laps minimum to commit to a 3 stopper
leaves you with a used tyre of a max age of 5laps?
Unless you can offset a extra lap on your new tyre, but then your only talking 2 laps at most given the new tyre will do 1 lap more life wise.
Any tyre with more than 6laps ager (7 or above) cant realistically be used in the GP
Which SHOULD leave the following allocations.