Isabel (Elizabeth) de Gaunt - Am I Missing Something?

She was originally entered into the record as "Matilda", so why/how was her name changed to "Isabel (Elizabeth)"?

MATILDA de Gand. Her parentage and marriage are noted in Domesday Descendants[997]. m WILLIAM de Welle of Wells and Claxby, Norfolk, son of WALTER FitzRademer & his wife ---

I think this proves she did exist, but the name is wrong (which is confusing).

According to Medlands, the only child of Matilda de Gand and WILLIAM de Welle of Wells and Claxby, Norfolk, was:

ISABEL (m. ROBERT de Tattershall, son of HUGH Brito [de Tattershall] & his wife)

https://fmg.ac/Projects/MedLands/engunttz.htm#_Toc51670251

https://fmg.ac/Projects/MedLands/ENGLISHNOBILITYMEDIEVAL3T-Z.htm#Ro...

Isabel and her husband had five Tattershall children: Philip, John, Robert, Roger, and Walter.

Here is Isabel, the daughter of Matilda de Gant and William of Welles and Claxby. But she's been assigned the wrong mother (Alice van Gant, Matilda/"Isabel" 's sister).

Isabel de Fitzwalter

According to Medlands (linked above) Robert de Tattershall m. ISABEL, daughter of WILLIAM FitzWalter de Welle of Wells and Claxby, Norfolk & his wife Matilda de Gand ([1134/35]-after 1212)

Somehow Matilda de Gant was renamed "Isabel" and her only child, a daughter named Isabel who married Robert de Tattershall -- was attributed to her sister, Alice (van Gant) de Mowbray.

Alice never married any Tattershall. She only married Ilbert de Lacy and Roger de Mowbray.