There's cross-reactivity, and they target both Influenza A and Influenza B strains (usually), so you'll get broader protection than strictly the strains most targeted by the vaccine. That said, you can ask the pharmacist for a copy of the FDA package insert, or google it yourself for the specific vaccine they're giving you. The package insert, under "DESCRIPTION" (Section 11), should tell you the precise strains that the antigens were developed from.

For example, google "FLUVIRIN fda package insert",and the one for the 2017/2018 flu season on page 8 you'll find "A/Singapore/GP1908/2015,IVR-180 (an A/Michigan/45/2015 (H1N1)pdm09- like virus; A/Hong Kong/4801/2014, NYMC X-263B (H3N2) (an A/Hong Kong/4801/2014- like virus); and B/Brisbane/60/2008, wild type (a B/Brisbane/60/2008-like virus)".

Google the same document for Fluzone quadrivalent, and you should find, for the 2020/2021 flu season, the strains "A/Guangdong-Maonan/SWL1536/2019 CNIC-1909 (H1N1), A/Hong Kong/2671/2019 IVR-208 (H3N2), B/Phuket/3073/2013 (B Yamagata lineage), and B/Washington/02/2019 (B Victoria lineage)" on pg 21.

In 2017, for example, the vaccine didn't work all that well, because of this exact problem. My dad, who lived in an eldercare facility, was confined to his room many days of the winter, which is something I sympathized with at the time, but sympathize a whole lot more with after this April's shelter-in-place order.

The deaths in the U.S. in 2017 were about 61,000, compared to the normal 40,000 or so.

Long story short: you don't know, but it's the best guess of those in charge of making that call.

There is no "usual flu vaccine", they make a new one twice a year, meant to address whatever strain is in circulation.