Interestingly, things start working again at 999. i.e. 
m/$mystrings[998]/;  # Fails
m/$mystrings[999]/;  # Works
m/$mystrings[1000]/; # Works

[download]
Deparse shows it's indeed parsed differently, but doesn't show why: 
> perl -MO=Deparse x
Global symbol "$mystrings" requires explicit package name at x line 10
+.
x had compilation errors.
use strict 'refs';
my(@mystrings) = 'string' x 200;
$mystrings[99];
"$mystrings[100]";
/$mystrings[999]/;
/${'mystrings'}[998]/;

[download]

Update: These values also work: 111, 222, 333, 444, 555, 666, 777, 888. And apparently above 1000 it's not simple either. The first working ones after 1000 are: 1110, 1111, 1113, 1114, 1115, 1116, 1117, 1118, 1119, 1131, 1141, 1151, 1161, 1171, 1181, 1191, 1311, 1333, 1411

Overall, there's 393 values from 0 to 10,000 for which it works. The rest fail.

In reply to Re: Match operator fails for elements 100 and higher by Crackers2
in thread Match operator fails for elements 100 and higher by thrasher

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