I remember Quick & Reilly. AT&T is complicated because of the Ma Bell breakup and recombinations over the years. If you are sure you purchased AT&T and not one of the Ma Bell pieces, I have records from 1994 onwards to mid 2005:
9/30/1994 price/shr $54.15
9/30/1996 Lucent spinoff, AT&T basis 72.01%
4/15/1999 3 for 2 split
7/9/2001 Wireless spinoff, AT&T basis 77.66%
11/18/2002 Comcast spinoff, AT&T basis 37.40%
11/18/2002 1 for 5 reverse split
11/18/2005 Merger with SBC, new name AT&T Inc. 0.77942 shrs new AT&T per old AT&T shr
Looking at
https://investors.att.com/stock-information/historical-stock-information/historical-stock-splits/att...
there were no more stock splits after 2005 and no spinoffs or mergers prior to the 4/5/2022 action.
Historical stock prices are also tricky because of the old AT&T Co vs the new AT&T Inc but
https://investors.att.com/stock-information/historical-stock-information/historical-quote/att-corp
is the right place to look.
Vanguard used a 72% AT&T and 28% WBD for the split of the AT&T cost basis as a result of the spinoff.
