Can I count FSC-certified MDF toward both MRc4 and MRc7?

MRc7 counts only new wood, and MRc4 counts recycled content, so there is no overlap in the credits. You must choose one credit, and not double-dip. For products with FSC Mix and recycled content claims—including many MDF products and complex assemblies that include MDF—LEED Interpretation #10372 clarifies that project teams have to choose which "environmental attribute" they will use to classify the product, and it (and its dollar value) will either go into an FSC "bucket" or into a recycled-content "bucket." 

Are there recycled content claims that I should be wary of?

Based on review comments that LEED users have reported, LEED reviewers are on the lookout for inaccurate recycled content claims in cases where a manufacturer is claiming pre-consumer recycled content for scrap material that comes off the end of a product line, and is put back in to the same line. According to common definitions, this should not be considered recycled content. This practice is common with certain kinds of glass, and metals like aluminum. Keep an eye on your documentation and do your best to make sure it is valid.

The manufacturer can't give me product-specific recycled content data, but they say that they fall within the national industry average. Can I use that?

No. Per LEED Interpretation #10246, recycled content claims must be specific to installed product. Average regional and national claims do not meet the credit requirements.

This Interpretation has been misinterpreted, however, to mean that recycled content figures must come from specific plants. That is not what USGBC intended. It is allowable to use a company- and product-specific national average, as long as the company has performed the necessary tracking to assure that that average is accurate at the product SKU level.

Why can’t I include mechanical, electrical and plumbing components in this credit? What if I consistently include MEP materials in the calculations for all of the MR credits I’m attempting?

LEED is very clear that no MEP or specialty items can be counted in the MR credit calculations. There are several reasons for this, including the fact that MEP items are very expensive relative to their weight, and including these materials skews the calculations and performance thresholds achieved. Also, LEED considers the performance of mechanical equipment paramount, and so consideration of these materials really falls under performance based energy and water credits.