One of BIBCO webinars had the following answer:

Our implementation of RDA in MARC 21 is following ISBD presentation 
outlined in Appendix D.1, but with some modifications. Please see 
specific instructions in the first LC-PCC PS 1.7.1 “Punctuation at the 
End of MARC Fields 245, 246-247, 250, 264, 300, 310/321, 362, 490”

1.) Fields 245, 250. If either field 245 or 250 does not end in a 
period, add one.

The above would mean that a period is not added when 250 fields end in a 
period.

Yuji Tosaka
Cataloging/Metadata Librarian
The College of New Jersey
Ewing, NJ 08628-0718
Phone: (609) 771-2156

On 9/30/2013 2:01 PM, Yan Liao wrote:
> I agree with your thought. If 250 ends with an abbreviation, no extra period should be added.
>
> -----Original Message-----
> From: Program for Cooperative Cataloging [mailto:[log in to unmask]] On Behalf Of Adam L. Schiff
> Sent: Saturday, September 28, 2013 7:55 PM
> To: [log in to unmask]
> Subject: [PCCLIST] Punctuation at end of 250 field
>
> Hi all, I've got a question regarding ending punctuation in the 250 field.
> RDA D.1.2.1 indicates that in ISBD display, an full stop would be added after an edition statement, even if the statement ends in an abbreviation:
>
> 3rd ed.. --
> not
> 3rd ed. --
>
> LC-PCC Policy Statement for 1.7.1 says: "If either field 245 or 250 does not end in a period, add one."
>
> Am I correct in my thinking that the implication of this policy statement is that if an edition statement ends in an abbreviation, a second period would NOT be added?  In other words, which of the following is expected in a PCC record?:
>
> 250 ## $a 3rd ed..
>     or
> 250 ## $a 3rd ed.
>
> [Note: the examples are predicated on the abbreviation being found and transcribed as is from the resource].
>
> Thanks,
>
> Adam
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Adam L. Schiff
> Principal Cataloger
> University of Washington Libraries
> Box 352900
> Seattle, WA 98195-2900
> (206) 543-8409
> (206) 685-8782 fax
> [log in to unmask]
> http://faculty.washington.edu/~aschiff
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>