Ticket solved_at missing when using incremental export api for older tickets

I'm trying to get the solved_at metric for all tickets (old and new) using the incremental export api and adding '&include=metric_sets'.  When I use it with a time range of the past four days it seems to work fine, but when I increase the time range up to the past 365 days, there are many instances where it doesn't get the solved_at metric. I can see the metrics when querying the old tickets individually (with the tickets endpoint), but then when I try to do it with the incremental export with a higher time range it doesn't work. Am I doing something wrong or is there possibly a problem? Thank you!!