It seems like actuarial literature overwhelmingly chooses one trend for the past and applies it to all years, and the same for projecting loss trend forward. Even with “one trend for the past, one trend for the future” there’s exactly one trend rate chosen for each, and it doesn’t vary by year. For most situations, this is probably OK. For the current economic environment, it arguably isn’t.
Is there literature out there that discusses choosing different trend rates by year, prior/future? I’m asking becuase with inflation by whatever measure you prefer running hotter than it has in prior years, at some point this year will become a prior year in ratemaking and choosing one and only one loss trend would seem to create problems. The same goes for projecting forward, if you think the current inflation rate is “transitory” and will slow before the effective date you’re choosing for changes or you’re doing planning and trying to project out a few years.