Time for a staffer to step in on the above mentioned issue. People have been doing exactly what you claim they have, this is true to be certain, but at the same time *most* "new" mods out there currently are nothing more than reskin/relight projects with slight changes from existing mods (most for example use the LA mod for their base-framework). For example "kitbashing" (taking model A from one mod, and putting it with model B from another mod and calling it a "new" vehicle), Reskinning existing units and claiming they are new, changing lightbars, etc.
Because of this it has become very sporadic for the "chain of ownership" to be retained, the parties that are initially altering the original mod are just as guilty in most cases as the end-offenders in not accurately compiling/maintaining credits/rights regarding everything they've used for their mods. This issue must as a community be addressed in order to retain any sort of reputation as a legitimate modding community.
The problem with your permission requirements is quite a large one, you did not create the original content used within your mod in it's entirety, so you cannot restrict usership of things that are open for use without explicitly listing the things you've changed that are forbidden to be used from within this mod, all other items must be credited just the same as you want people to provide you with such courtesy. IF for example you've taken someone else's model from another mod and have reskinned it only, then you have a right to restrict usership of the skin, but if the original model was available for anyone to use, then any user may use that model just the same as you were able to, with all corresponding original author restrictions applied. Such is why modders in this community MUST be more aware of the fact that others may have contributed to a work and you SHOULD be aware of who these person(s) are prior to using something! This falls onto the mod developers to populate a readme/document with all pertaining credits and restrictions related to content in which they've used so that people are aware when using "your" mod who really did what and which individuals must be contacted specifically regarding content someone wishes to use.
Just because something is in your mod does not give you rights over the item in it's entirety, if you reskinned it, you have rights over the skin alteration, if you altered the model significantly then you may retain rights over the model, (for example most people are just taking existing lightbars from one mod and putting them onto another mod's vehicles, so really the original authors of both the lightbar and the model base should be credited FIRST, then the alteration modder should get credit for putting them together). Without these successive "chains" of permissions properly documented, you have a steep battle for justifying your "rights" over an article released, if you are unwilling/unable to complete this chain of documentation, then how is it fair to expect people to obey your permission/credit conditions, when you opted to not show the same courtesy to those who you've used content from?
Either everyone as a community needs to get better in this respect, or people should cease using other's content all together, if users are unwilling or unable to give other's credit where it's due then it is not reasonable to believe you should have that extended courtesy for yourself. This post is not directed at this author or topic specifically, but as a community-wide advisement because this statement had to be made, and the community as a whole needs to reflect upon it and alter their conduct as required in order to maintain a reputable community.. The alternative is that people will cease to let users use their content and the community as a whole will suffer as a result of people being unprofessional about how they conduct themselves with other's works (remember someone put in the time to make the items that you've had the benefit of, they deserve their credit where it's due). Personally I do not feel it is much to ask for proper permissions/credit chains to be maintained within this community, particularly from users who believe they should have credit/permission rights themselves, if modders won't take the step to be courteous to those who made the content they've used, they have no right to be upset when the same occurs to them.