Older reviews aren’t showing
The short answer
The widget collects the 100 most recent reviews from each source, on every plan. Anything older sits outside that window and will not appear, no matter what you set.
Filters and sorting operate within those 100, which is why filtering can return fewer results than expected.
Why an old review has vanished
It has not been removed — it has fallen out of the window as newer ones arrived. On a business collecting thirty reviews a month, a review from four months ago is already gone from the widget while remaining perfectly visible on Google.
Why a filter returns almost nothing
Set a five-star-only filter on a source whose recent hundred happen to include a rough patch, and the widget shows what survives — which can be far fewer than your lifetime five-star count suggests. The filter is not broken; the pool it draws from is the recent hundred.
What to do about it
If a specific older review matters, add it by hand as a custom entry alongside the collected ones. If you want more depth generally, the limit is the same on every plan and voting on the wishlist is the honest answer.