Can you share the link to them? I believe it’s something like “beeminder.com/[your username]/[your goalname]”. You can test whether that shows what you want it to show by copying it into a private browser (or logging out).
The statistics tab on your goal’s webpage will tell you the current total, which you could capture regularly in a spreadsheet and do the comparison that way. I think it’d be a cool addition (UVI!) to that tab’s goal progress section to show how much has been accomplished in the last month/year/whatever.
Also, in the settings tab, under graph settings you can specify an ‘x-min’ of the start date to display on the graph, so you can eyeball estimate the starting total for whatever period.