Graf's record of 186 straight weeks isn't mathematically safe for Fed; he will make 161 weeks on top on Feb 26th, which means that he needs another 26 weeks - half a year - to surpass Steffi. From now until then he roughly has Dubai F+IW+Miami+Halle+Wimbly+finals at RG, MC and Rome+Toronto+US Open adding up to roughly 5300 points, while his lead over Nadal is 3345 points. So if Roger gets injured until September, and Nadal defends his hc and clay points while knocked out in R1 in Wimbly and RG, Steffi will still have the record. Pretty unlikely scenario though.
I guess Fed won't be mathematically guaranteed of 187 straight weeks before Halle.