I feel like for the most part I can drop in and resume as long as I know right off that it is a Simon & John story. It may take me a few minutes to recall the prior entry ("oh yeah, he took her stomach") but as you note, I do try to read most of the entries each week.

I think as long as each story can stand alone fairly well you don't need to recap; some folks who do serials post a link to prior entries at the top or bottom, or hyperlink a name (i_17bingo typically does this). It's up to you if you think doing so is necessary or not. Thanks for asking!