I have a 2015 iMac with a 1TB fusion drive. Currently 425 Gb are in use. I'm using a 1Tb external HD for TM. Disk utility is telling me that 800GB are in use on the external drive and 200 GB are free. The problem is that TM only lets me go back in time to yesterday evening. There are no files available before yesterday. I noticed the same problem back in May/June and so I reformatted the external HD thinking that would fix the problem but clearly it hasn't. I would think I should have several weeks that I could go back in time if needed. Any thoughts on what could be going on here?