I think I have at last found a site with a fairly "clear" explanation:

http://www.unesco.org/webworld/mdm/czech_digitization/doc/fo...

....
10. Applicable foliation and Applicable pagination statements
The numbering of pages (this numbering comes from the numbers which were directly entered into the manuscript) which is referenced by literature and at the same time does not correspond with the actual order of the pages of the manuscript, is described by the Applicable foliation or Applicable pagination statements. Both the Applicable foliation statement and the Foliation statement can, at the same time, be a part of the description. Likewise, the Applicable pagination statement and the Pagination statement can, at the same time, be part of the description. This means that Applicable pagination can only occur with Pagination and Applicable foliation can occur only with Foliation.

We would like to mention again, that the contents of the Applicable foliation and Applicable pagination statements come from the numbers which are directly inserted into the manuscript. The pages or sheets of the manuscript are usually numbered after a larger number, after 10 for example. In an ideal situation, the manuscript will contain all of its original sheets and, at the same time, it will be accurately numbered. This means that the Applicable foliation and the Applicable pagination statements totally correspond with the Foliation and Pagination. In this case, only the Foliation of Pagination statements can occur in the description. If, however, the above mentioned conditions are not met, the Applicable foliation and Applicable pagination statements have one important characteristic that makes them different from the Pagination and Foliation. This characteristic is that each page or sheet number directly entered into the manuscript exactly corresponds with the contents of the Applicable foliation and Applicable pagination statements in the appropriate record. In the case that some numbers written into the manuscript are too close to each other thanks to the loss of pages or a mistake which happened during the numbering of the manuscript, some of the entries will be omitted in the contents of the Applicable foliation or Applicable pagination statements.

On the other hand, if there are too many sheets between the numbered pages then some entries are repeated in the contents of the Applicable foliation or Applicable pagination statements. In order to differentiate between the repeated entries Latin numerals are added to them (for example, 1 bis, 1 ter,...).

Important characteristics of the Applicable foliation and Applicable pagination statements.
The Applicable foliation statement can have the same contents as the Foliation statement but the contents must correspond to the following forms
NUMBER LATIN_NUMERAL r
NUMBER LATIN_NUMERAL v

if the number is written using Arabic numerals. At least one space must be used to separate the number from the Latin numeral and the Latin numeral from the letter. Only the following Latin numerals are allowed: bis (twice), ter (three times), quatries (four times), *quinquies* (five times), sesties (six times), septies (seven times), octies (eight times), nonies (nine times), decies (ten times). For example, FC, BF, IIv, 99r, 99v, 99 bis r, 99 bis v, 99 ter r, ..., all correspond to the Applicable foliation statement, whereas II bisr, FC ter, II bis, 1, quatries 5r, 5r *quinquies* and 6quinquiesr are all incorrect.


2. The Applicable pagination statement can have the same contents as
the Foliation statement but the contents must correspond to the following
form

NUMBER LATIN_NUMERAL

if the number is written using Arabic numerals. At least one space must be used to separate the number from the Latin numeral. Only the Latin numerals bis, ter, quatries, ..., decies are allowed. For example, FC, FS, I, IV, 99, 99 bis, 99 ter, ..., all correspond to the Applicable foliation statement, whereas entries II sesties, FS ter, IIr, 2 ter v, 1bis are all incorrect.

It is necessary to maintain the following order in the contents of Applicable foliation:


FC, FS,
Ir, Iv, IIr, IIv, IIIr, IIIv, ..., ICr, ICv,

1r, 1v, 1 bis r, 1 bis v, 1 ter r, 1 ter v, 1 quatries r, ..., 1 nonies v, 1 decies r, 1 decies v,

2r, 2v, 2 bis r, 2 bis v, 2 ter r, 2 ter v, ..., 2 decies r, 2 decies v,

3r, 3v, ..., 3 bis r, 3 bis v, ...., 3 decies,

...,

..., 999 decies r, 999 decies v,

Ir, Iv, IIr, IIv, IIIr, IIIv, ..., ICr, ICv,

BS, BC.



The order of this example shows that 20r cannot come before 10r, 99 ter r cannot come before 99 bis r and 3 ter r cannot come after 3 ter v.



3. It is necessary to maintain the following order in the contents
of Applicable pagination:


FC, FS,
I, II, III, IV, V, ..., IC,

1, 1 bis, 1 ter, 1 quatries, 1 *quinquies*, ..., 1 nonies, 1 decies,

2, 2 bis, 2 ter, 1 quatries, 1 *quinquies*, ..., 1 nonies, 1 decies,

2, 3 bis, ..., 3 ter, ..., 3 decies,

...,

..., 999 nonies, 999 decies,

I, II, III, IV, V, ..., IC,


BS, BC.



The order of this example shows that 20 cannot come before 10 and 99 bis cannot come after 99 ter.



Note: From the above mentioned characteristics of the Applicable foliation and Applicable pagination statements, it can be concluded that individual entries can occur only one time.



HTH

Regards,

Rich