Would the Israel's 50th Jubilee Anniversary really be
a definitive when it commemorates an anniversary ?
Yes it is. In much the same way that, for example, GB issued a Millenium Definitive which formed part of the Machin series.
Israel have only ever issued definitives in large sheet format and never issued a commemorative as an NVI.
Israel has down the years seen many Definitive series, some lasting longer than others. In more recent times, the National Flag has formed part of the design.
The stamp shown [up there somewhere] was issued in the Jubilee year but does not show this on the design itself.
If one thinks about it, there are many definitive stamps and series that do not look like definitives. Some examples shown in earlier posts are proof of this.
All Definitive stamps [in Israel at least] have a title.
Londonbus1....good question !