Estimates for "undetectable" planets in extra-solar systems
This is a partial answer. It is partial because this is an active area of research, with this very topic as one of the prime questions, second I've only chased down the estimates from one method; microlensing, because this method is not biased toward large (in size and mass) planets in close orbits around small stars.

The microlensing method is biased toward more massive planets in Jupiter like orbits i.e. cold planets. It is biased toward distant planets about stars much closer toward the galactic center. This is important because stars there have lower concentrations of heavy elements need to make planets. It is equally sensitive to planets round all sorts of stars, and even free floating planets. It can detect down to Earth mass planets.

Here is a link to a technical summary of the method. The part you are most interested in is section 4.1.3 pages 23. Microlensing Searches for Exoplanets Yiannis Tsapras
This poster paper has a summary plot Fig 3 of planet occurrence rates from various methods Poster: Planet frequency from microlensing observations Arnaund Caasan
There is also a link to an archive of papers on the subject: NASA archive: Planet Occurrence Rate Papers

I do a quick summary of the main results: (microlensing perspective).
Estimating the biases, combined with actual detections it is possible to estimate (or put limits on) the numbers of planets and how theoccurence depends on mass, distance from star.
Snow line == distance from star where water remains frozen. In our solar system it is between Mars and Jupiter. Jupiter's moons have lots of ice. Dimmer stars this is closer in.
1 AU = Earth-Sun distance

Number of planets beyond snow line (Jupiter and beyond in our solar system) is 7 times greater than close in hot planets. In the distance range 0.5 to 10 Au of 20% of stars have Jupiters. 50% have Neptunes, 60% have super earths. There are many stars with more than one planet. So there is about one planet for every star in the galaxy. At least!. About 1/6th of stars with planets have a solar analog (massive planets like Jupiter and Saturn with room for small rocky planets close in).