Invariants of limit key polynomials

Let $\nu$ be a valuation of arbitrary rank on the polynomial ring $K[x]$ with coefficients in a field $K$. We prove comparison theorems between MacLane-Vaqui'e key polynomials for valuations $\mu \le \nu$ and abstract key polynomials for $\nu$. Also, some results on invariants attached to limit key polynomials are obtained. In particular, if $\mathrm{char}(K)=0$ we show that all limit key polynomials of unbounded continuous MacLane chains have numerical character equal to one.