Are there strategies for notating chords like this?
The bass note matters a lot for the chord sound. It's rare to have upper structure notes in the bass. It's not because they necessarily sound bad, but because the bass note is so dominating that it may no longer sound as an upper structure. In your case, Bb could be the root of a Bb chord, could be a third of a G chord, maybe could be a b5 of an E chord, but is rather unlikely to be the b13 of a D chord, or the b9 of an A chord.
This gives us three candidates:
- Eø7add4/Bb (or Em7b5add4/Bb)
As PiedPiper suggests, one more possibility is for the chord to be missing the root, a.k.a. rootless voicing. C13 is a really good suggestion! It includes 3: E, and b7: Bb, which are the most important tensions, and then some more. Also, importantly, it doesn't include F, which is 4, which often blurs the chord's identity.
But how to choose one of those? This depends on the context.
Ask yourself "what does it sound like?" What other, simpler chord you could play instead to move the harmony in a similar way. This may mean removing additional notes from your chord, but also adding some which are omitted. Could you replace it with a C triad? This depends on the context, the key, the preceding chords, and most importantly, the following ones. How the harmony flows, what resolves to what?
What you propose, E-7(𝄫5)/B♭, isn't right. There isn't really such a thing as a 𝄫5. A perfect fourth sounds like a perfect fourth. Em7b5 is quite a common chord, on the other hand.
Within the context, I would interpret the whole progression as:
Em7b5add4/Bb Am7 Gm7 Dmadd4add2
Why this choice? Please compare it with this simplified progression:
This is of course subjective, but to me it seems these simple chords grasp the essence of the progression, and what you have is just more "color" notes. The V→I relations between E and A, and then G and D dominate the movement, especially given the lack of other strong dissonances and resolutions.
The last chord feels quite unresolved, due to the added 4, but within the context I hear it as Dm.