to be more precise, the question should be "should singapore be included in the list of historical unrecognized states between the period 1st september 1963 through the 16th of september 1963?"
from as recent as 2012 to as far back as 1736, there's a list of historical unrecognized states and/or countries which existed temporarily (less than weeks or months), existed for a period of years and subsequently re-absorbed by larger states or political entities, existed for a period of years/decades and re-emerged with a new name and state/country, still continue to exist today.
the earliest notable state in such a list is the kingdom of corsica (birthplace of my favorite hegemon, napoleon), and the year of secession from the republic of genoa was 1736. from 1755 to 1769, it became the corsican republic and was subsequently annexed by france. corsica is part of france to this day.
the latest notable state in this list is azawad, 2012 to present, a controlled territory in northern mali by ansar dine. it is the current hotbed of "terror" activities (near algeria).
closer to sg, and in the middle of the list, is the lanfang republic. the lanfang republic was established by chinese settlers and immigrants in indonesia from 1777 to 1784, and was known to be a tributary state of qing china. the dutch took control and added it as part of the indonesian colonies.
since there are so many tiongs in sg, the prc was formerly referred to as the chinese soviet republic from 1931 to 1937 even though china was under kmt rule and referred to as the republic of china.
closer to home in sg was the unrecognized state of tamil eelam (1983 to 2009). we know it's now re-absorbed by sri lanka.
there was also the philippine republic from 1899 to 1901. it was an independent state by self-declaration on june 12, 1898 up to the same year on december 10, and that was when spain ceded her philippines' colonies to the u.s. after the conclusion of the spanish-american war. it was formerly established as an independent country with a new constitution in january 23, 1899. it fought against the u.s. in a war of independence and lost in 1901. today the philippine republic is part of the philippines.
question is. how cum the 16-day pre-federation independent singapore is not on the list even though she is now the republic of singapore?