Where can I find my routine backup files

1. I would like to locate the actual backup files in a path set out as in one of the tutorials:
drive letter:\computer name\Backup Set YYYY-MM-DD HHMMSS
so I can confirm that backups are actually being made.

2. I have searched my entire computer for "backup set" but found only two, both within a folder (I assume) dated 2015-03-30-235528):

3. At 30 March, 03-30-235528 (the same as the assumed enclosing folder!), 5.4 GB, 114 files, and at 4 April, 04-05-190000 (9.4 MB, 212 files). As expected the second one was smaller because it would have backed up changed files only.

4. But, I did a backup manually on 26 April as correctly confirmed by Control Panel > System & Security > Backup and Restore, which reported "Files in Libraries and personal folders for all users and system image." The same window reports that the file was 70.5 GB (which is much bigger than the earlier backups).

5. Why is the 26 April backup not included in the list at 3 above? And

6. Also, why does Properties > Previous versions for the second (4 April) backup report "There are no previous versions available"? The 30 March is a previous backup.

This doesn't give me the assurance that I was looking for that backups are actually being made and are available for use in an emergency.

Thanks for any help.