This was posted on the Renfrew list a few days ago - I tend to ignore any entries which are not C,M or P.

LDS & IGI Information...
(copied from another list)

Batch numbers beginning with A, L, M17, M18,T0, T90, 69409-
indicate LDS Temple records and have limited access.

Batch numbers beginning with C, E, J, K, M (except M17 and
M18), P, T5, 725, 744, 745, 754- indicate extracted birth,
christening or marriage record.

E- Batches: Replace the "E" with an " M" and find the "M-"
batch number in the IGI Batch Number Index.

T-5-Batches: Just above the IGI entry with a "T-5-" batch
number, you will find a nearly identical IGI entry with a
different batch number. Use that batch number to find the
source.

725-, 745-, and 754- Batches: These batches are extracted
indexes, usually with no more information. Names may be
listed alphabetically ...Surnames A - O are on film 543896.
P - Z are on film 543897."

Batch numbers beginning with F, T96, T998, T9990, and all
digit numbers such as 8434961 [except beginning with 725-,
744-, 745-, 754- as above] are forms submitted to the
Ancestral File by individuals. They may be a Family Group
Record, an Individual Entry or Marriage Entry. The
microfilms can be ordered and photocopies can be made.
Submitters' names and addresses may be outdated.

F- Batches: Check the forms to understand the data. Some
information is estimated or added and may be different from
what you expect.

T96- Batches: This is a correction to an existing record.