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.
Mess with the Bull - you get the horns.