IRS proposed regs. issued 4/11/2008 referred to 1.430(f)-1© a number of times. For example:

(3) Plan assets equal or exceed funding target. For any plan year in which the
value of plan assets (as reduced to reflect the subtraction of certain funding balances
as provided under §1.430(f)-1©, but not below zero) equals or exceeds the funding
target of the plan for the plan year, the minimum required contribution for that plan
year is equal to the target normal cost of the plan for the plan year reduced (but not
below zero) by that excess.

While I believe this means subtract credit balances (that's what the statute says), it would be helpful to be able to see this reference and this poor old soul can't find it.

Here's the fed register.

I may have missed it, but I don't think that the section in question appears in that document. (Though it refers to it several times.)

Look at the August 2007 regulations, roughly page 60 of 133.

Here's a cut&paste of the section.

© Effect of balances on plan assets--(1) In general. In the case of any plan with
a prefunding balance or a funding standard carryover balance, the amount of those
balances must be subtracted from the value of plan assets for purposes of sections 430
and 436, except as provided in paragraphs ©(2), ©(3), and ©(4) of this section.
(2) Subtraction of balances in determining new shortfall amortization base--(i)
Prefunding balance. For purposes of determining whether a plan is exempt from the
requirement to establish a new shortfall amortization base under section 430©(5), the
amount of the prefunding balance is subtracted from the value of plan assets only if an
election under paragraph (d) of this section to use the prefunding balance to offset the
minimum required contribution is made for the plan year.
(ii) Funding standard carryover balance. For purposes of determining whether a
plan is exempt from the requirement to establish a new shortfall amortization base
under section 430©(5), the funding standard carryover balance is not subtracted from
the value of plan assets regardless of whether any portion of either the funding standard
carryover balance or the prefunding balance is used to offset the minimum required
contribution for the plan year under paragraph (d) of this section.
(3) Special rule for certain binding agreements with PBGC. If there is in effect for
a plan year a binding written agreement with the Pension Benefit Guaranty Corporation
(PBGC) which provides that all or a portion of the prefunding balance or funding
standard carryover balance (or both balances) is not available to offset the minimum
required contribution for a plan year, that specified amount is not subtracted from the
value of plan assets for purposes of determining the funding shortfall under section
430©(4). ... (more follows)