SPY closed @ $412.20, but its $412 covered call was not assigned against me.

Yesterday, option expiration Friday, 4/21/23, my 100 shares of SPY closed @ $412.20.  I was pleased because I wanted my 4/21/23 SPY $412 covered call to be assigned, forcing me to sell my 100 SPY @ $412.  But today I saw that it wasn't assigned.  It expired worthless & I still own the 100 SPY @ $412.20 - actually, a 20 cent benefit to me.

When I worked in the industry, & this happened to my clients, they might protest, "My covered call closed in the money by 20 cents but I wasn't forced to sell my stock.  Did your broker/dealer (Fidelity, until my retirement) stiff me?" 

We often say with the above SPY covered call, "If SPY closes on expiration date above $412, your $412 covered call will be assigned, forcing you to sell your SPY @ exactly $412." That's a "pretty fair rule" of covered call selling.

But to be more accurate, for this $412 covered call to be assigned against a seller like me, a buyer of the 4/21/23 SPY $412 call has to exercise his right to buy SPY @ exactly $412.  Then, the Options Clearing Corporation randomly assigns this exercise to a broker/dealer like Fidelity that has this covered call among its clientele.  Then the broker/dealer like Fidelity randomly assigns it to a client that has sold this covered call, like me.  If any of these $412 calls were exercised yesterday by the owner of the call, I was never randomly picked for an assignment. 

Yesterday, SPY traded above & below $412 all day.  At 3:51pm ET, it was at $411.93, but then closed at $412.20.  During the day, a buyer of this $412 call might have asked himself, "Why would I exercise my call to buy SPY @ $412 when I can simply buy it in the market when it's trading at $411.50?"

When I sell a SPY $412 covered call, I'm creating a contract.  Because I received a premium, I accepted an obligation to sell my SPY @ $412 if the call option is exercised AND assigned to me.