1.401(a)(4)-8(d)(1)(i) says "Under the floor-offset arrangement,... all or part of the employee's acount balance ..." - which anticipates partial offsets.
Compare that to 1.401(a)(26)-5(a)(2)(iii)(A)(3) - "The contributions or benefits under the plan that are used to offset". This doesn't seem to anticipate an offset by part of a plan.
The June 6, 2002 Memo refers to "the benefit provided under a profit sharing plan". This also doesn't seem to anticipate an offset by part of a plan.
The 7/17/2007 Memo refers to offset a number of times:
The first paragraph has "an offset by other plans".
The third paragraph has "the benefit provided under a profit-sharing plan" - again, no mention of part of a plan. However, it then has "if the offset applies for some participants" which must anticipate splitting a plan into parts.
The fourth paragraph then reverts to "the benefit provided under a profit-sharing plan" and "the benefit provided by another plan".
Therefore, one could argue either way whether it is permissible to offset by part of a PS plan.
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If it is not permissible to offset by part of a PS plan, then (2)'s reference to "the benefits under the offsetting plan" means the same thing as the offset. However, if partial offsets are OK, then it appears that (2)'s reference ought to be interpreted to mean the offsetting benefits, rather than the benefits of the plan as a whole. This would be consistent with the earlier references to "the offset", "an offset" and "the benefit provided".
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While it seems prudent to get a determination letter, is this even possible with the staggered system now in place?