How does the 100 metre Ethernet limit apply when I am using patch leads?

The familiar 100m figure is for the complete copper channel, not for each individual cable in it.

A conventional structured channel is based around up to 90m of permanent-link cabling plus the patch and equipment cords.

Long stranded patch cords also have greater insertion loss than solid horizontal cable, so the neat 90-plus-10 picture should not be treated as a licence to assemble any collection of cords that happens to total 100m.