I dont think so. Some motors are full manifold vacuum to the vacuum advance, others are ported vacuum to the advance. A 235 is ported vacuum and typically there is no vacuum at idle, hense no need to disconnect the adcance to set the timing. Others are full manifold and the advance must be disconnected to set the timing.
For a small block chevy, 38 to 40 degrees total timining is about the range you typically see. This is set using a combination of mechanical advance and initial advance. A typical chevy distributor has 12-14 degrees of mechanical advance, none of which is in play at idle. 12-14 at the distributor equated to 24-28 at the motor. To get to say 38 degrees total, you set the timing, with the vacuum advance disconnected and plugged, at 10 degrees before TDC. That gets you the 38.
Now, once your vacuum advance is hooked back up, and connected theoretically to full manifold vacuum, it will add what ever the can was made to add. Different GM can numbers equate to different advance totals and different levels of vacuum. So its not unusual to see the vaccum advance add a few degrees, in this case 19, at idle.
As you put your foot into the gas pedal, the vacuum drops and the vacuum advance is not adding any timing to the equation. This happens pertty quickly which is why that much advance at idel is not much of a concern. Throttle opens, vacuum goes away, vacuum advance goes away. At WOT there will likely be 0 vacuum so it does not come into play at all. In between, various levels of advance will play into th4e equation depending on the amount of vaccum applied to the advance diaphram. The vacuum advance is helpful at part throttle and crusing so its good to have. Here is a little light reading on the subject.https://www.motortrend.com/how-to/1607-tune-your-vacuum-advance-for-better-drivability/http://www.langdonsstovebolt.com/tech/vacuum-advance-and-why-you-want-it/