you answered your own question. That particular tracker is current thru Feb 5, 2021. Delta was detected in OK, Mar/Apr 2021 but wasn’t listed as a VOC until May 4, 2021. Genomic tracking for B.1.167/AY, scroll down to bar graph and highlight variant on right to change bar graph:
https://covid.cdc.gov/covid-data-tracker/#variant-proportions
So it’s the bar graph at the bottom and the selector to the right, not the second page at all. K.