I admit it is real handwavy but it goes to the consideration of how confident are we in the data. That is, how "clear" is the data. Can we see signals within the signal that we are not expecting, or can we only see what we are expecting to see?
My "math" to suggest one might be able to pickup a gw crossing another gw 1 ly away is a general figuring that a gw gradient stayed coherent after traveling 1.3billion lys and is "spread out" in terms of power in an inversed cubed type of way that results in the wave (initially with the force of the mass of multiple suns turned instantly to energy) only having the power to distort space the width of a partial proton over the distance leveraged by the experiment, yet we can read the effect that this distortion has on space through monitoring the interference of some EM waves that took two orthogonal routes to the detector...whereas the gw we sense today HAD to either have been crossed by or is soon to be crossed by another GW that we just saw or are about to see. So the impulse, the wave of one gw should be embedded in the next.
Not in any measurable way, as has been discussed. The chirp is a light-second in length. 3 x 10^5 km. If there's any effect, you stretch or shrink that by a part in 10^-18. The pulse becomes ~10^-16 m shorter or longer. Its duration changes by nanoseconds. Undetectable.
And this fluctuation, this "interference" had to happen within a couple lys of here because the two waves crossed earth within a year of each other. So space is curved within curved space, and the interaction should still have some coherence because relatively few other GWs have had a chance to add or subtract their impulse, and the interaction had to be a billion times closer than the original gradients.
But again, I am trying to box in the answer to the thread question. Either we can pick up GWs or we can't. If we can, then we can make further study of them, and possibly use them as probes of space...able to in essence "feel" the universe around us. And while having a fourth, or building 12, would be stupid if we cannot detect GWs, if we CAN detect GWs we should be able to learn a lot more about gravity than we know today, by studying in detail, GW waves. If we can see a strong one from 1.3 billion lys, mathwise, we should be able to see a weak one from 1 ly.
There will be no GWs from a LY away since there isn't any appreciable mass at that distance, doing anything that would emit them. A little while ago we discussed scaling. Perhaps you could go back and review that. You need a huge amount of mass, and appreciable acceleration, to get anything we could detect. Only a handful of the binary pulsars we can observe emit enough gravitational radiation to potentially see their orbits degrade over the years, and that's not nearly enough to detect with LIGO.
I am having a hard time, mentally. figuring what the intersection of two GWs would look like in space. It would not be one event, but an infinite number of events happening continually, at an infinite number of locations, within, at a particular instant, that area of space where the two expanding shells coexisted. So while one GW passes through a spot on Earth in a sec, another portion of that expanding shell has to already be passing through another "close" GW...so depending on how precisely we can see one wave embedded in the prior, or the next, we might, with 12 detectors, be able to map gravity waves that passed through already, before we had any detectors up. (by reading the record of other gws on the passing one)
Ripples on a pond might be a good starter for visualizing interference. The waves do not become embedded. You have no basis for continuing to make that claim.