Cost basis importance when in 0% LTCG bracket?

Given the following... • Early retired, withdrawing from taxable brokerage • Invested in VFIAX (Vanguard S&P500 mutual fund) • 0% federal LTCG bracket, 3% state • Have older shares for which Vanguard does not know cost basis • Want to keep everything as simple as possible ...Is there any reason I should be concerned that I went with Average Cost when I did my first ever stock sale? I'm *thinking* it should be fine, since I can't see the advantage in micromanaging lots for tax efficiency when my cap gains taxes are going to be almost zero (for now and the foreseeable future, I'm a very low spender). Searching around I read a lot of comments that weren't in favor of Average Cost, but it seemed like the context was higher-spending individuals concerned about tax efficiency. But I still thought I'd ask for a sanity check on whether I'm missing some major problems. Thanks.