The second match in the flipflop operator /startpat/ ... /endpat/ destroys the captured Number ($1) of the left side. Consider these shell snippets.

# no regex in end pattern of flipflop
$ echo "Curve4 " | perl -lne 'if (/Curve(\d+)/ ... eof) {print $1}'
4

# code similar to your example
$ echo "Curve4 " | perl -lne 'if (/Curve(\d+)/ ... /^\s*/) {print $1}'
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