Altay was ready for serial production in, at least, october of 2016 according to Ali Koc (
https://t24.com.tr/haber/altay-tanki-seri-uretim-icin-hazir,369990).
But we were getting embargoed before 2016 (or at the very least in 2016). Austrian government blocked AVL to give technical assistance to Tumosan regarding the development of local engine. This article was written in October of 2015 (cancelation of Tumosan tank engine project):
https://www.milliyet.com.tr/ekonomi/altay-in-kalbine-avusturya-katkisi-2135167
Austria, Netherlands, Germany, etc all had the same policies regarding the defamation of Turkey in their media (this has been going on since2012/2013 at least, where I first noticed this in the Netherlands). That Austria blocked technical support, we could tentatively conclude that Germany was already blocking (or would've blocked) the procurement of engine's, as Germany's policies go hand in hand with Austria.
This article, written in march of 2017, talks about how an embargo by the German's would effect the Turkish military industry:
Alman hükümetinin birçok defa Türkiye'ye silah ihracatını engellediğinin ortaya çıkması iki ülke arasında yeni bir gerginliğe neden oldu. Uzmanlara göre, Türkiye savunma konusunda eksen kayması yaşayabilir.
www.dw.com
It goes on to say that the German state blocked several products since 2010.
From article: "2010-2015 yılları arasında kimi savunma malzemelerinin Türkiye'ye ihracatına sekiz kez izin vermeyen Alman hükümetinin, 2016 Kasımı'ndan bu yana da tam 11 kez silah ihracatını engellediğinin ortaya çıkması gözleri Türkiye'ye çevirdi."
This sentence suggests that Germany went to full embargo from Otcober 2016 onward (the same month Altay was confirmed to be ready for serial production by Ali Koc).
It said that the embargo's were on small arms, bullets and some defence products in the next paragraph of the article, but we know now that these embargoes included (or was on the verge to include) tank engine's (probably considered as a 'defence product').
Ali Koc (from top source): "Düğmeye basıldığı andan itibaren seri üretime 18-22 ay içinde başlayacağız."
So when SSM had given Otokar the green light, it would've taken Otokar 18 to 22 months to start serial production. Which even in this case would've been within the scope of Germany's ban. According to Ali Koc's quote, the production line for the Altay tank would've been ready within 18 to 22 month's. So the actual work on the first tank would've begun somewhere around april 2019.
However, Ali Koc's quote is a bit ambiguous. Maybe he meant the first tank would roll out in 18 to 22 months. In that case the first tank would be ready in april of 2019 (18 months). But still in both cases, the serial production could not have avoided the German ban on engine's.
According to this info, even if serial production of Altay began in 2016, it would've still had the same problems it is facing today, regarding engine's. What Turkish government should've done, according to this info, was to stock up the 250 engine's and transmissions before the 2010's. But in 2010, Altay was in it's 3'rd year of R&D, buying and stocking up so many engine's that early on would've been a risky move. Maybe they could've procured the engine's between 2010 to 2015, but Germany was already blocking some exports back then so no guarentee that the engine's would not have been blocked.
They can't prevent you from using them. But depending on how it's written in the contract, if Turkey for example is in breach of how the subsystem is used, than the foreign exporter can refuse to sell you the subsystem or any subcomponents for the subsystem. An example of this is Wescam camera's for TB2. The contract stated that these were designated to be used by Turkey only (specifically Turk Deniz Kuvvetleri). But since they were also used in the Karabagh conflict, Canada imposed embargoe's to Turkey, as Turkey was in breach of contract in this case. Tolga Ozbek explains it from the 4 minute mark onwards:
In other words, it all depends on what's agreed and written in the contract when procuring systems and subsystems.