Q about accounting for long term capital gains, losses, etc.

A personal question of a practical (mechanical/procedural/tactical) nature if I may please [I hope this is an appropriate place to ask it]. Since my query relates to stock in T most likely we're talking leveraging losses instead of gains here. LOL

I currently hold some shares of T and some of its spinoffs beginning with my initial employment back in mid-1988. Many of these were initially acquired via Employee Discount (should probably call it a fire sale) Plan in my first several years there along with what got spawned from exercising a handful of none too generous merit-based options granted along the way and of course their subsequent starry-eyed drunken-sailor-like M&A involving CMCSA, WBD, and so forth. Quite a none too distinguished legacy there … anyhow I'm understandaby at the lifecycle stage post-retirement where I want to basically clean up my portfolio and get my financial affairs overall in workmanlike shape.

Bottom line, how am I best advised to proceed with clearing out all the debris stemming from my employment remaining for far too long in my brokerage account[except some dividends along the way which have already been taxed [along with my patience]? —- while I tried to conscientiously retain relevant paperwork and documentation [pay stubs, official related correspondence, account statements, etc.] along the way but locating some or all of it is shall we say challenging since I worked there beginning in long-ago 1988. Is there a way to objectively and to the satisfaction of the IRS determine what possible sort of basis to use when I dump this stuff out at the mercy of the market now and hopefully use the proceeds [no matter how meager] more gainfully and hopefully in a more satisfying manner?

Clearly I'm not talking millions or billions of here (quite far from it) but it's certainly more money involved than I'd prefer to leave on the table especially for Uncle Sam to then nibble on.

Above was a wordy (but hopefully not overly verbose) view of where I'm at and next term steps I feel I'm ready to take. Thanks for any suggestions especially since I can't be the first person to ask this sort of question!