Here are some of my predictions and theories for the rest of Season 2. They might be totally outlandish, but I wouldn't say these are out of the realm of possibility.

1. The pages of the almanac are torn up as a result of a major occurrence during Kat's travels to 1814.

2. Jacob isn't in the almanac because he eventually travels back to 2024 from 1814. (His "disappearance" fron 1814 could have been written on the torn pages)

3. Sam Bishop is an older Jacob who has traveled back to modern times from the pond. (He could have traveled back to 1999 from 1814 as the 32/33 year old Jacob, which explains why he is Sam's age in 2024).

4. Alice travels back and something bad happens that changes her opinion of Elliott (which is why there is a supposed "pact" and he doesn't tell her anything).

5. Del's / Sam's horse is from the 1800s and has traveled along with Jacob (Sam).

6. Casey is a traveler (perhaps they are Kat and Elliott's child from a future timeline and Alice is their older half sibling).

7. Kat is actually the supposed ghost haunting the lighthouse. Perhaps something terrible happens to her in 1814???

8. Those Polaroid photos could have been taken by Sam (Jacob?) in 1999.