In August, a Blackstone Group dealmaking team gathered one day at 2:30 pm in a conference room overlooking Park Avenue to clink beers and celebrate the anniversary of the moment Blackstone signed papers to purchase its business.

The team, which buys stakes in private equity funds, was acquired from Credit Suisse in 2013 following European banking rules that were implemented after the global market meltdown. Those rules, the bank said at the time, made it cumbersome to own the business and prompted it to hang a for-sale sign on it.