Not straightforwardly, and the comparison depends almost entirely on what the fresh
comparator is.
Freezing itself preserves nutrients well. Once the product is below minus eighteen
degrees Celsius, the chemical and enzymatic reactions that degrade vitamins are very
slow. The measurable losses in a frozen vegetable happen at two other points: the
blanching step, where water-soluble vitamins – vitamin C most notably, and some B
vitamins – leach into the blanch water, and long storage, where slow oxidative losses
accumulate.
The fresh comparator, meanwhile, is losing nutrients continuously from the moment of
harvest, and how much depends on how long it spent in distribution and at what
temperature. A vegetable frozen within hours of harvest and a vegetable that spent a
week in ambient distribution are not in the same condition when they reach the
consumer, whatever the label says.
That is why published comparisons vary so much and why blanket claims in either
direction should be treated with suspicion. The defensible statement is that a
well-processed frozen vegetable is nutritionally comparable to a fresh one, and can be
better than a fresh one that has been in the chain for several days.
For a commercial specification, none of this is directly usable. If a nutrition claim
matters to your customer, it has to be substantiated on the actual finished product by
analysis, not inferred from the category.