Private-equity managers are increasingly opening their data rooms for investors ahead of their latest fundraising efforts without communicating to those investors exactly how big those funds will be.

Historically, private-equity firms specified a fund’s target before they launched official marketing efforts in order to give prospective investors a sense of the size and scope of the portfolio they plan to build. As demand for private equity has grown and investors scramble to secure allocations with top performers, veteran private-equity firms can afford to delay communicating such goals, if not dispense with them altogether.