If you watch the entire series you’ll see that Agents of SHIELD firmly established itself as MCU canon & explained it’s own divergence from it already. Hopefully any attempt to bring these characters back will do their research to acknowledge this. I still can’t believe how many people tuned out & never gave this series a chance. It continued to reinvent itself year after year to keep things interesting & they ended on their own .

I think some of the missing elements in the show are to keep us guessing. I haven’t researched the original series dialogue/details, but maybe Harry & Capt Matthew’s history started pre-Miami Metro, and could lead to flashback stories about their past after Matthew’s comes to the precinct. If they even debated the possibility that Original Sin would be successful enough for continued seasons, they’d know Harry will die, and some of the missing links could create more opportunities to keep Slater’s continued presence relevant.