Now hear me out... The writers have always made the show very misleading... 2420 was supposedly when they were hurt, but there was a lot of hurt before that as well and 2420 phase was relatively not that problematic. Also they were supposed to fall in love at 2521 but they were already in love by then, plus they were apart for a lot of time of those years.
My theory is that heedo named her shop 2521 bcoz it was the only year they were really apart and in doubt about their relationship... she named it that so she always remember how sad it was to be apart from yijin but her feelings of concern and love for yijin was always more, and that seperation made her sure of her feelings even more
The writers have always made the show very misleading... 2420 was supposedly when they were hurt, but there was a lot of hurt before that as well and 2420 phase was relatively not that problematic.
Also they were supposed to fall in love at 2521 but they were already in love by then, plus they were apart for a lot of time of those years.
My theory is that heedo named her shop 2521 bcoz it was the only year they were really apart and in doubt about their relationship... she named it that so she always remember how sad it was to be apart from yijin but her feelings of concern and love for yijin was always more, and that seperation made her sure of her feelings even more