Many countries have almost given up on coins. Their last known circulation. Series may hardly be of any guidance. Some of them are Vietnam, Lao, Cambodia, Bhuran, Myanmar, Liberia, Iraq, Nigeria, Mongolia etc.
Pakistan has changed all designs in last few years.
Sri Lanka is due for a new stainless series this year.
Nigeria had a 3 coin series in 2006 but now abandoned. Similarly, Myanmar, Iraq and Afghanistan had a new series not very long ago and they were quite a change from earlier series.
Sierra Leone, Cuba and Liberia announced some series but there does not seem to be any progress, as also with Iceland.
Each country is a specific case and needs to be studied in detail.
Pakistan will never change its obverse but reverse has been changed significantly.
UAE may follow Saudi Arabia which recently revised its series .
Bangladesh too revised its series with effigy of Sheikh Mujibur Rehman, not very long ago.
Swaziland has changed its obverse with change of King as well as ageing effigy.
Oman revised its Coat of Arms few years back, very minor changes, like Russia two years back and Romania this year.