...and don't forget that you're counting something slightly different.

tabcount( "a\tb\tc", 'three fields' );
tabcount( "a\tb\t",  'two fields, trailing tab' );
tabcount( "\tb\tc",  'two fields, leading tab' );

sub tabcount {
    my ( $tabby, $descr ) = @_;

    print "*** $descr ***\n";
    printf "scalar split %d\n", scalar split( /\t/, $tabby);
    printf "tr/\\t/:      %d\n", $tabby =~ tr/\t//;
}
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Output:

*** three fields ***
scalar split 3
tr/\t/:      2
*** two fields, trailing tab ***
scalar split 2
tr/\t/:      2
*** two fields, leading tab ***
scalar split 3
tr/\t/:      2
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