  In certain pulsar timing experiments, where observations are scheduled
approximately periodically (e.g. daily), timing models with significantly
different frequencies (including but not limited to glitch models with
different frequency increments) return near-equivalent timing residuals. The
average scheduling aperiodicity divided by the phase error due to
time-of-arrival uncertainties is a useful indicator of when the degeneracy is
important. Synthetic data are used to explore the effect of this degeneracy
systematically. It is found that phase-coherent tempo2 or temponest-based
approaches are biased sometimes toward reporting small glitch sizes regardless
of the true glitch size. Local estimates of the spin frequency alleviate this
bias. A hidden Markov model is free from bias towards small glitches and
announces explicitly the existence of multiple glitch solutions but sometimes
fails to recover the correct glitch size. Two glitches in the UTMOST public
data release are re-assessed, one in PSR J1709$-$4429 at MJD 58178 and the
other in PSR J1452$-$6036 at MJD 58600. The estimated fractional frequency jump
in PSR J1709$-$4429 is revised upward from $\Delta f/f = (54.6\pm 1.0) \times
10^{-9}$ to $\Delta f/f = (2432.2 \pm 0.1) \times 10^{-9}$ with the aid of
additional data from the Parkes radio telescope. We find that the available
UTMOST data for PSR J1452$-$6036 are consistent with $\Delta f/f = 270 \times
10^{-9} + N/(fT)$ with $N = 0,1,2$, where $T \approx 1\,\text{sidereal day}$ is
the observation scheduling period. Data from the Parkes radio telescope can be
included, and the $N = 0$ case is selected unambiguously with a combined
dataset.
