One great benefit from conferences is the questions that are posed ... they sometimes identify things that weren't previously considered.
Effective 1 January 2010, firms must revalue portfolios for large cash flows. Okay, fine. AND, unless you revalue for ALL flows, you can't then revalue for SOME that fall below what you define as large. Example: you use Modified Dietz on a monthly basis; your definition of large is 10%; you get an 8% flow in, you cannot revalue. Okay, clear enough.
What happens if you have a composite, that is made up of mutual funds and separate accounts, where the funds are valued daily and the funds use monthly Modified Dietz? Looks like we have a problem :-(
Clearly, some guidance is needed. I would favor an amendment whereby in these cases, where you have some funds that you value daily and some that you value monthly, then the "large" rule will only apply to those that are valued monthly. There may be some holes here ... we'll have to see.