Could a worker do SEPP under IRC 72(t) on a prior employer's 401(k) while continuing to keep his current 401(k) and 403(b)?

[Guest JurisPrude]

Example, we have a job hopper from academe and the private sector,... say a former law professor... He starts as an atty a gets a 401(k), then becomes a prof and gets a 403(b) -- then leaves to work in management consulting and gets a 401(a) DC plan.

He is still young, could he do a 72(t) on the first account, -- the 401(k) only and keep the 403(b) untouched? Can he still keep getting contributions in his curremnt 401(a) plan?