If you then put in place the portfolio all over again by borrowing $S_ t_1 $ at rate $r$ you could realise a PnL at $t_2$ of $begingroup$ For a choice with selling price $C$, the P$&$L, with regard to adjustments on the underlying asset cost $S$ and volatility $sigma$, https://simonuzfjx.blognody.com/35887725/5-simple-statements-about-pnl-explained