“NASDAQ lost 80% of its value from peak. “
You said they lost 90=99% from the pre-bubble values:
” ... when many tech stocks lost 90% to 99% of their pre-bubble value ... “
“Many tech stocks” is not the average NASDAQ. Those that lost 90% to 99% (and went out of business or got delisted) contributed to NASDAQ losing 90% from peak.