Lost Access to Older Time Machine Backups Owing to Disk Reformat

I hadn't been using Time Machine for a long time because I didn't have an extra backup disk for it (I had and still have one that I use for clone backups), but I bought another disk this past March and started doing Time Machine backups again. I haven't tried to retrieve any old files until today, July 29, when I found I couldn't go back beyond June 6, and I assumed this was because I had reformatted my disk back around then. Inspection showed that access permissions apparently had something to do with this, as the Desktop, Documents, Dropbox, Library, Movies, Music, and Pictures folders in my home directory (but not the other ones) were marked at the lower right by a red circle with a horizontal white line in it, and Get Info said "You have no access". Can this be corrected, and if so how? I followed the A4 sequence on a Time Machine troubleshooting page, deleting and recreating the preferences file. I opened the Backups.backupdb folder on the backup disk and it shows only one Mac with backups going back to March when I started.

If it's impossible to fix this, I hope someone will quickly tell me how to wipe Time Machine clean and start all over (so I don't have to look it up :-). I found the file I wanted on a different external volume, there's not much else if anything I think I'm going to want in the Time Machine backups from March, and I'd rather not have old backups around that I can't access. Thanks!