According to Yfull , one person with same subclade . Ytree states MRCA 1200 ybp . That would be 820 AD . Big Y matches at FTDNA give Cornwall for their earliest ancestor . A Wiki article on a Charles Henry Gatty states they were previously Gatty from Insubria .

The earliest UK IGI entry for Gatty is in 1573 in Cornwall . Via My heritage , based on a match to my father , there's a Thomas Gattye 1440-1491 in Trefugalon .

Where was the family between 820 to 1440/1573 AD I'm wondering ? Was it a one step move from Insubria to Cornwall ,or a gradual set of steps ?