Confused about bibliography in old books

A quick search of the current Bodleian catalogue turns up this record.

Selecting the 'find & request' tab indicates that the three volumes are still available with call numbers 55.b.59-61. Thus, it would appear that the bibliography is specifying call numbers in the different libraries (much as modern bibliographies list DOIs!).

To expand on @avid's answer: those numbers very likely refer to manuscripts, incunabula, or other rare or unique items.

Specific index references are necessary for a number of reasons, even if a single library may have multiple copies of a work:

• Titles get many variations over time, may be spelled multiple ways or in different languages.
• Dates are often sketchy at best, but oftentimes may be century estimates (even if there's a date, if it's a manuscript it may be a copy from a different era).
• Manuscript tend to have important errors, variations, and marginalia, that distinguish copies, so we need to know exact tomes/scrolls/etc that were used.

As an aside, you will probably not get copies via ILL, but you may be able to get the source library to scan them for a nominal fee (or they may already be scanned and freely available—check online especially for large national libraries).