Bailey is on the NF of the South Platte (NFSP). It's flows come primarily from Denver Water's (DW) operation of the Roberts tunnel, which delivers water from Lake Dillon to the NFSP, where it flows to Strontia Springs Reservoir and is then delivered to DW's Foothills Water Treatment Plant. The South Platte proper (SP) joins the NFSP just above Strontia Springs at Waterton Canyon. DW also uses Cheeseman Reservoir and SP sources to deliver water to Strontia Springs Reservoir. When DW operates the Roberts Tunnel depends on many factors including: water demand in Denver, reservoir storage levels and streamflows on both West and East slope, operation and maintenance considerations, native flows in the SP, etc. It's really complex.
The best thing you can do to get a read on Bailey flows is keep an eye on deepsouth's Bailey/Roberts updates and look at the actual Roberts Tunnel gage on the DWR website.
Ironically, the water that isn't in Bailey is now in Gore...but on a molecule for molecule basis, not a flow basis.