Yeah, there's a difference between linear phase (which you can achieve with a causal filter, i.e. one that is running in real-time) and constant-phase, which requires that you have more or less the whole signal before you filter it (you can approximate it to the extent you're willing to add more latency).

Good addition.

I mentioned the forward/backward bit as this was a way to achieve linear phase in analog times eith more conventional filters (although the cost here was even higher with the additional added noise floor due to tape noise ad the extra work involved).