In his Le Gavroche cookbook, Michel Roux Jr. has a recipe for Gigot d'agneau de sept heures where he marinates the leg of lamb for at least a week.
However I see that e.g. the US Department of Health and Human Services, says that you should store a roast of lamb for no more than 3-5 days in your refrigerator in their Cold Food Storage Chart.
Now, I feel that I should be able to trust both of these sources, but obviously I can't follow both of their advice. I kinda assume the storage chart might have some leeway, since the department absolutely do not want anyone to get sick from following their advice, so they add in a safety margin? Then again it'd suck if I gave my guests food poisoning, even if I followed the recipe of a food professional.
Are there any other considerations I should make? Could I get away with a somewhat shorter period of marinating the lamb? Any advice would be most appreciated.