There is no guide! But it should be 100% (high concentration of a standard) depending on your expected concentration and sample matrix.

Hi you can refer to pharmacopoeia, some may differ from each other but most of the time the recovery range from 90% to 110% or at least 95%. I don't have one with me when I'm writing this comment so I'm not sure whether there is a chapter for multivitamin product, but I can recommend you search for individual vitamin chapter in pharmacopoeia to get the an idea the limit for recovery for each vitamin (if multivitamin chapter is not available).

Besides that you have to know what level is the concentration of vitamin in your product as recovery percentage required may differ base on the concentration of vitamin in your product.

It is best that you start with United State Pharmacopoeia or British Pharmacopoeia as both are more widely accepted.

Please look at the following below links which may help you in your analysis:

https://www.chempap.org/file_access.php?file=593a202.pdf

https://www.researchgate.net/publication/11594588_Extraction_of_fat-soluble_vitamins

https://www.academia.edu/22915031/Fat-soluble_vitamin_extraction_by_analytical_supercritical_carbon_dioxide

Thanks